This proposal by an established investigator addresses topic 5: alternative to estrogen therapy. Postmenopausal osteoporosis is by far the most common cause of bone loss and therefore, a search for potential therapies is of vital concern. Recent reports have indicated that several classes of estrogen-like compound phytoestrogens; pharmacologically and structurally similar to tamoxifen, an estrogen agonist/antagonist) have bone protective properties. However, the efficacy of lignans, a potent group of phytoestrogens containing a 2,3- dibenzylbutane structure has not been studied with respect to bone. Flaxseed is the richest source of precursors to lignans that can be easily incorporated in the diets of humans. The findings of our recent clinical trial suggest that flaxseed may exert a positive effect on bone and calcium homeostasis. We propose a randomized trial to test the hypothesis that flaxseed will have beneficial effects on bone mass in postmenopausal women who have not been on estrogen replacement therapy (HRT) for at least one year prior to the start of the study. In a three-month study, 58 postmenopausal (2-10 years) women will be randomly assigned to one of the two regimens: flaxseed (40 g/daily) or control (40 g/daily). These regimens will be packaged individually in powdered form. Postmenopausal women who meet the inclusion criteria will be recruited from our existing subject pool, primary care and specialty clinics, cooperative extension service organizations, and by advertisement at large. In order to provide some protection against rapid bone loss, especially to those who might be nearly osteoporotic, all study participants will receive 1,000 mg elemental calcium plus 400 IU vitamin D daily. Since assessing bone density in this short-term study is not meaningful, the efficacy of treatment will be assessed by measuring serum and urinary indices of bone turnover. Medical and reproductive history and dietary and lifestyle variables related to bone health or estrogen use will be obtained at baseline and will be monitored throughout the study. Sample size is adequate to permit detection of about 20percent difference between groups in change in N- telopeptide, one of the best urinary markers of bone resorption, with 0.8 power at significance level = 0.05, allowing for 10percent attrition. Analysis of variance techniques will be used to assess treatment (flaxseed vs. control) differences. Values measured at the three-month mark will be divided by the baseline values to adjust for person-to-person variability. Ratios of bone formation marker values to bone resorption marker values will be calculated and analyzed in an effort to combine both attributes into one measurement. Selected covariables will be included to adjust for potential confounders. Multiple regression models will be constructed to determine to what extent certain variables are associated with indices of bone turnover.